DESCRIPTION: The role that humoral immune responses play in the pathogenesis of periodontal disease is unclear. Results from several studies suggest that periodontopathogen-specific antibodies are protective in nature, while other data indicate that these molecules are active participants in the pathogenic process. In an attempt to clarify the role of antibody in periodontal disease, this proposal will focus on the antibody response to the leukotoxin (LTX) produced by Actinobacillus actinomycetemcomitans. It is the hypothesis that the time course of acquisition of a functional anti-LTX antibody response is critical to determining the outcome of infection. The goal of the proposed studies is to evaluate the molecular and functional heterogeneity of the human antibody response to the LTX. In Specific Aim 1, epitope mapping will be used to define the LTX binding specificities of 130 serum samples longitudinally collected from 10 localized juvenile periodontitis patients. These studies will enable them to identify the immunogenic epitopes of the LTX molecule. In Specific Aim 2, the functional properties of LTX-reactive antibody will be evaluated. Synthetic peptides corresponding to the amino acid sequence of immunogenic determinants identified in Specific Aim 1 will be used to affinity purify reactive antibody. An in vitro assay will be used to determine whether antibody directed at each of these epitopes neutralizes LTX bioactivity. The resultant data should provide information defining those regions of the LTX that elicit neutralizing responses. Additionally, they will be in a position to evaluate whether the presence of LTX-specific neutralizing antibody is in any way related to the progression and/or resolution of LJP. By characterizing and comparing the anti-LTX responses prior to disease onset at the time of clinical breakdown, and during the recovery phase of each patient, they will be able to address this question. In Specific Aim 3, "neutralizing" epitopes identified in Aim 2 will be used to establish LTX-specific human B cell lines. It is their long-term goal to identify the genes encoding LTX neutralizing antibodies and delineate the immunogenetic factors that may play an important role in determining susceptibility to periodontal bacterial infection and subsequent disease progression.